bool query(vector<string> line) // line is a vector of strings where each ellement is a word in the command line
{
	if (relation_name(line[0]))// relation name
	{ 
		if(line[1]=="<-")
		{	
			if(expr(line, 2)//expr
			{
				return true;
			}
		}
	}
	return false;
}
relation_name(string name)
{	int i=0;
	if(name[0]==NULL)
	{	
		return false;
	}
	while(name[i]!=NULL)
	{ 
		if (!(name[i].isAlpha()||name[i].isDigit()))
		{
			return false
		}
	}
		return true;
		
					
			

bool comand(string line)
{
//open-cmd
	if(line == "open-cmd")
	{
		open-cmd(relation-name);
	}
//close-cmd
	if(line == "close-cmd")
	{
		close-cmd(relation-name);
	}
//write-cmd
	if(line == "write-cmd")
	{
		write-cmd(relation-name);
	}
//exit-cmd
	if(line == "exit-cmd")
	{
		exit-cmd();
	}
//show-cmd
	if(line == "show-cmd")
	{
		show-cmd(relation-name);
	}
//create-cmd
	if(line == "create-cmd")
	{
		create-cmd(relation-name);
	}
//update-cmd
	if(line == "update-cmd")
	{
		update-cmd(relation-name);
	}
//insert-cmd
	if(line == "insert-cmd")
	{
		insert-cmd(relation-name);
	}
//delete-cmd
	if(line == "delete-cmd")
	{
		delete-cmd(relation-name);
	}
}

bool open-cmd()
{
	ifstream ifile(relation-name)
	if(ifile)
		return true;
	else
		return false;
}
bool close-cmd(relation-name)
{
	ifstream ifile(relation-name)
	if(ifile)
		return true;
	else
		return false;
}
bool write-cmd(relation-name)
{
	ifstream ifile(relation-name)
	if(ifile)
		return true;
	else
		return false;
}
bool exit-cmd()
{
	return true;
}
bool show-cmd()
{
	return atomic-expr;
}
bool create-cmd(relation-name)
{
	if(relation-name && typed-attribute-list && attribute-list)
	{
		return true;
	}
	else
		return false;
}
bool update-cmd(relation-name)
{
	if(relation-name && attribute-name && literal)
		return true;
	else
		return false
}
bool insert-cmd(relation-name)
{
	ifstream ifile(relation-name)
	if((ifile && literal) || (ifile && expr) )
		return true;
	else
		return false;
	
}
bool delete-cmd(relation-name)
{
	ifstream ifile(relation-name)
	if(ifile && condition)
		return true;
	else
		return false;
}
bool typed-attribute-list()
{
	type();
}
bool type()
{
	integer();
}
bool integer()
{
	digit();
}